Log periodic electron discharge device



Sept. 8, 1970 H. L. THAL, JR

LOG PERIODIC ELECTRON DISCHARGE DEV-ICE Filed Sept. 29. 1966 4SheetsSheot 1 do w on an an 3 an BE e INVENTOR HERBERT L.THAL ,JR. BY WHIS ATTORNEY.

Sept. 8, 19

H. L. THAL, JR

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LOG PERIODIC ELECTRON DISCHARGE DEVICE Filed Sept. 29, 1966 4Sheets-Sheet :5

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Se t. 8, 1970 H. L. THAL, JR

LOG PERIODIC ELECTRON DISCHARGE DEVICE Filed Sept. 29. 1966 4Sheets-Sheet 1.

INVENTOR: HERBERT 'L. .THAL,JR.

Hl ATTORNEY.

United States Patent U.S. Cl. 3153.6 26 Claims ABSTRACT OF THEDISCLOSURE An electron beam log periodic device is disclosed which inone form is an R-F amplifier including a slow wave circuit defining anelectron beam path therethrough. The slow wave circuit tapers in a logperiodic manner and the electron beam which passes therethrough is alsocorrespondingly tapered in a log periodic manner. An input signal iscoupled into the circuit to selectively energize a region therein basedon the input signal, and the beam is modulated. This modulated beampasses into another part of the circuit to selectively energize a regiontherein and amplified power is taken off the circuit.

This invention relates to a log periodic electron discharge device andmore particularly to a log periodic electron beam device includinginteraction between an interaction structure having interactioncharacteristics varying progressively therealong in a log periodicmanner and an electron beam passing therethrough, whose interactioncharacteristics vary progressively therealong in a log periodic manner.Optimum interaction takes place at selected regions along theinteraction structure depending on the frequency characteristics of aninput signal wave to provide, for example, a very high R-F power outputover a wide frequency band.

Extensive efforts have been expended to increase the operating bandwidthof microwave or R-F tubes in general. Particularly, high power R-F tubessuch as velocity and/ or density modulated electron beam tubes,including klystrons and traveling wave tubes, are generally compromisesbetween inherent bandwidth limitations and power output. For example, arnulticavity velocity modulated electron beam klystron usually has avery high power output in a range of up to several megawatts but with amaximum relative bandwidth of only about On the other hand typicaltraveling wave tubes generally have lesser power output but increasedbandwidth. Hybrid combinations of klystrons and traveling wave tubes mayprovide more bandwidth but with a sacrifice of other primeconsiderations such as output, uniformity, gain, etc. Due to thecontinuous development of more sophisticated electron apparatus, thereis an increasing demand for example for a single tube type having both auniform high power output and a wide frequency band.

Accordingly, it is an object of this invention to provide an improvedelectron beam interaction device.

It is another object of this invention to provide an improved logperiodic electron beam modulating device.

It is yet another object of this invention to provide an improved logperiodic R-F amplifier having a high power output over a wide frequencyband.

It is still another object of this invention to provide an improved logperiodic klystron type amplifier.

It is yet another object of this invention to provide an improved logperiodic slow wave circuit type amplifier.

It is still another object of this invention to provide a log periodicR-F amplifier utilizing a log periodic electron beam in combinationtherewith.

It is still another object of this invention to provide a log periodicamplifier having a tapering interaction structure and a tapering beamtherein.

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It is a further object of this invention to provide an improved logperiodic amplifier having a conical or frustoconical interactionstructure with a correlated conical or frustoconical electron beampassing therein.

It is yet another object of this invention to provide improvedtermination means for a log periodic interaction structure.

It has been discovered that a log periodic principle as applied to bothan interaction structure and an electron beam therein provides a moreeificient wide band device such as an R-F amplifier. In this invention,log periodic or log periodic manner are terms applied to an array ofinteraction circuits, elements, or regions which are dimensioned andpositioned such that electrical properties, such as impedance, at eachelement or region repeat periodically with the logarithm of an operatingfrequency, e.g., input signal frequency.

Briefly described, this invention in one of its preferred forms,comprises an interaction structure, including a slow wave circuit, whoseinteraction characteristics therealong vary progressively in a logperiodic man ner. An electron beam, whose effective interactioncharacteristics, in combination with the interaction structure, varytherealong progressively in a log periodic manner, is caused to passthrough the interaction structure in a manner such that the beam andstructure variances occur in the same direction. More specifically, onepreferred embodiment of this invention includes a series of spacedresonant klystron type or reentrant cavities and interaction gapsinteracting with a tapering electron beam passing therethrough. Eachofthe resonant klystron cavities in the series spaced array diifers in itseffective size and resonance in geometric progression from a largerresonant cavity to a smaller resonant cavity along the extended arraywhile the traversing electron beam correspondingly differs.

Log periodic is a term applied to either the interaction structure, theelectron beam, or both, whose defined characteristics therealong varyperiodically in geometric progression. The variance is predicated to alarge extent on dimensions. For example, in an extended array ofklystron type resonant cavities, each cavity is pref erably an exactduplicate of its preceding cavity with the exception that significantdimensions of all parts are reduced or increased as the case may be. Inthis respect the drift tubes also become progressively smaller betweenadjacent cavities both in diameter and length, and the combined overallreduction provides geometrical axial reductions of successiveinteraction gaps. In a slow wave circuit utilizing a helix, which is aspecial case of a periodic structure, for example, successive sectionsor regions are progressively reduced in diameter while turn densityincreases. The thickness of the wire and lateral dimension may alsoprogressively decrease. In combination the electron beam in eitherinstance tapers or decreases in cross section along the interactionstructure in the same direction.

In copending application Ser. No. 582,879, Wilbur, filed concurrentlyherewith, and assigned to the same assignee as the present invention,there is disclosed an electron beam device having the log periodic orgeometric progression applied only to an interaction structure and notto the beam.

This invention will be better understood when taken in connection withthe following description and the drawings in which FIG. 1 is a crosssectional illustration of one preferred embodiment of this invention asa log periodic klystron amplifier;

FIG. 2 is a cross sectional illustration of a further preferredembodiment of this invention as applied to an alternate log periodicklystron type device;

FIG. 3 is a frequency-phase diagram for the invention of FIG. 2;

FIG. 4 is another modification of this invention with the log periodicprinciple applied to a helix-type traveling wave tube device.

FIG. 5 is a modification of this invention combining the circuits ofFIGS. 1 and 4.

Referring now to FIG. 1, there is illustrated the log periodic principleof this invention as incorporated in a klystron type amplifier 10.Klystron type amplifier includes an interaction structure comprising anextended array of a number of adjacent coaxial cylindrical resonantcavities 11 through 26 distributed between an illustrated taperedsection 27 having cavities 11 through 18 therein, and an illustratedcylindrical section 28 having cavities 19 through 26 therein. Theextended array of cavities of this invention in the tapered section 27is based upon or embodies a logarithmic progression which provides eachsucceeding cavity with geometrically progressively decreasing operatingcharacteristics with respect to its resonance. In one form of thisinvention the logarithmic periodicity and geometric progression isapplied, in one sense, with each adjacent cavity being essentially aduplicate in all respects with a preceding cavity with the exception ofbeing smaller in significant dimensions by a constant factor which maybe denoted as p. This logarithmic periodicity with geometric progressionis preferably extended over a substantial number of adjacent cavities inthe klystron type amplifier 10 and preferably in excess of about threecavities. The logarithmic factor p as applied to a cavity diameter, forexample, would include a first cavity having a diameter of, for example,1.0 with the next succeeding cavity having the same position diameter of0.9, and the next succeeding cavity of 0.81 etc. Accordingly, thegeometric progression or the log factor p in such an instance is definedas 0.9 or alternately as a continuous 10% decrease along the array. Thesame factor is applied to all significant dimensions of the cavities inthe geometric series.

One form of defined interaction structure in accordance with the logperiodic principle includes each cavity 11 through 18 of the logperiodic interaction structure having common or partition walls 29through 36 of decreasing diameter with respect to the defining side orbounding wall 37. By reason of the decreasing diameters of the partitionwalls and the axial distance therebetween, the side wall 37 takes on, asa surface of revolution, a conical or tapering or frustoconicalconfiguration. This taper, exaggerated in FIG. 1 for the purpose ofclarity, includes tapering from a larger diameter at the input end 38 ofthe klystron type amplifier 10 to a smaller diameter in a directiontoward the output end 39 of the klystron type amplifier 10. Eachsucceeding cavity may be smaller than a preceding cavity in stepwiseprogression so that a series of short cylindrical bounding wall 37sections approximate the smooth taper in the same manner as a number ofshort straight lines may define a curve or circle. The notedapproximation is related to configuration only since the stepprogression is a geometric progression.

The geometric progression also includes adjacent cavities whose densityor number of cavities per unit length of interaction structure increasesfrom the input end 38 toward the output end 39'. For example, the axialdimension between adjacent cavity partition walls also decreases in adirection from the input end 38 to the output end 39. The axial distancebetween adjacent walls 30 and 31 for example is less than thecorresponding distance between walls 29 and 30.

Cavities 11 through 18 also include as a part of their cavityconstruction, short tubular transverse wall sections 40 through 48 whichare defined as reentrant or klystronlike drift tubes. Each of thesereentrant tubes is spaced from preceding and succeeding reentrant tubesto provide well-known klystron type interaction gaps 49 through 56.Reentrant tubes 40 through 48 are formed as short frustoconical sectionsto define a longitudinal tapering channel or electron beampath 57 Whosetaper follows the log periodic principle as described for the cavities11 through 18. However, the reentrant tubes may be short cylindricalsections of decreasing diameters in geometric progression to approximatethe taper. The interaction gaps 49 through 5-6 which are defined betweenadjacent reentrant tube sections are also involved in the geometricprogression principle in that their axial spacings also decrease fromthe input end of the tube 38 toward the output end 39 of the tube 10.These gaps decrease and become smaller in geometric progression in thesame manner as the cavities become smaller.

It is understood that providing cavities in the geometric progression asdescribed will soon involve a very great number of very smalldimensions. For example, and theoretically speaking, the number and sizedecrease of cavities approaches infinity at the apex of the taper of aconical section. When the number of cavities becomes disproportionatelylarge and of disproportionately smaller sizes, their effectivenessbecomes greatly decreased and an arbitrary but compromising point isreached where the device 10 is terminated and the array of cavities isterminated or ended substantially before the apex point may be reached.This results in the need for a termination of a kind which will reduceend losses and other undesirable effects from the great number ofdisproportionately small caviti s.

The axial section 27 of device 10 which is illustrated as the taperedsection may be terminated in the form of a frustum where the definedarray of cavities cease substantially before the apex is reached, asillustrated and described in the mentioned copending application, or bya smooth tapering frustrum or apex section having a number of identicalcavities with the exception of diameters.

A preferred method of termination includes a short cylindrical section28 having a number of succeeding equal cavities therein not embodyingthe geometric progression. For example, section 28 includes a pluralityof cavity resonators 19 through 26 all of which are similar in allrespects in that their partition walls 58 through 65, drift tubes 66through 73, and interaction gaps 74 through 81, .etc., are all equal toone another. The number of resonant cavities in any terminatingcylindrical section not embodying the log periodic progression isusually less than the number of cavities in the tapered section 27 butmay be of an equal or greater number. A klystron amplifier asillustrated should have at least three cavities in section 27.

A common cavity wall such as wall 36 or a cavity volume may be thetransition section between sections 27 and 28 depending on the number ofcavities employed and their arrangement. It is desirable to have thelast cavity in section 28 such as cavity 26 pass through the projectedapex 84 of the tapered or conical wall 37, as indicated by theintersection of cone lines 82 and 83. Lines 82 and 8-3 are theequivalents of extension lines of tapered Wall 37 and pass through ordefine apex 84. For example, as illustrated in FIG. 1, the last wall 65of cavity 26 passes through the projected apex point 84.

In order to provide an electron beam passing through channel 57, anelectron gun structure 85 is utilized at the input end 38 of klystron10, and a corresponding electron collector 86 as well known in the artis utilized at the output end of the klystron 10. Electron gun structure85 is exemplary of a number of suitable gun structures including forexample the gun structure as disclosed in US. Pat. 3,046,442 Cook. Seealso J. R. Pierce, Theory and Design of Electron Beams, Nostrand Co.,Inc., New York, NY. l949. In FIG. 1, electron gun structrue 85 includesa cylindrical electrically insulating section 87 which is mountedconcentrically on the input wall 88 adjacent cavity 11 and is alsoconcentric to the electron beam channel 57. A transverse wall 89 isattached to section 87 to support the electron gun emitter 90 therein.Electron gun emitter 90 as known in the art includes an electronemissive surface usually including a combination of a barium compoundand a refractory metal matrix. This surface which is denoted as surface91 in FIG. 1 is of a concave design ordinarily as large as or largerthan the beam channel and is suitably supported by wall 92 from thetransverse wall 89. A filamentary type electrical heater element 93 issuitably positioned adjacent concave surface member 91 to raise thetemperature thereof for copious electron emission. Filamentary heater 93includes electrical elements 94 which project through wall 89 in aninsulating electrical relationship and are connected to a suitablesource of power such as for example battery 95.

An electrical shroud or forming structure 96 having an outwardly flaredlip 97 thereon circumferentially surrounds the concave emissive surfacemember 91 and 1S electrically connected to the transverse wall 89. Anannular block member 98 defines the entry portion of the electron beampath 57 and is positioned concentrically thereto and concentrically withthe structure of electron gun emitter 90. These structures 96 and 98,and their adjacent flared surfaces 97 and 99, are so formed so that theelectric field existing therebetween exerts a controlling infiuence onthe electron beam to control the beam shape as it enters member channel57.

The collector 86 as well as the remaining interium parts of the klystrondevice are electrically conductive so that transverse wall 89 isconnected to the negative side of a suitable source of power, such asbattery 100 while the cavities structure and the collector '86 areconnected to the positive side of the battery 100. Electrons aretherefore emitted from surface 91 and are suitably formed by shroud 96and annular block 98 and the electrical field therebetween as anelectron beam 101 to pass down the electron beam path 57 and to becollected by the collector 86. Collector 86 may be a suitable blockmember defining an electron collecting cavity or cavity surface 102therein, and may also have suitable cooling means associated therewithas known in the art.

It is an important feature of this invention that the electron beam 101passing through section 27 have effective interaction characteristicswhich vary axially along the beam from the input end 38 of device 10toward the output end 39 in a log periodic manner. The log periodicinteraction characteristics of beam 101 include the overall effects ofthe beam on the interaction structure, as compared to a cylindrical beamin a cylindrical path, as well as the successive beam portions alongsuccessive resonant cavities or regions of the interaction structure. Inone form of this invention the log periodic characteristics are embodiedin electron beam 101 by having the electron beam is provided orgenerated and defined in the form of a tapering, frustoconical orconical taper cross section. For example, the electron beam 101 of thisinvention includes a tapering or frustoconical beam whose equallyaxially spaced cross sections would include cross sections ofprogressively decreasing diameters in the manner described for thepartition walls 29 through 36 for example of the tapered section 27. Thetapered or frustoconical beam is one means to provide the proper degreeand kind of interaction at each interaction gap.

It should be noted that a tapered beam such as a conical beam may notper se be described as including the log periodic principle in thatthere are no given or defined increments of length. The log periodicprinciple arises when the beam is in the geometric progression sectionof the interaction structure. In this environment, when viewingsucceeding transverse sections of the circuit and beam separately, thelog periodic and geometric progression is evidenced by succeedingincrements of the beam of smaller dimensions, i.e., diameter and length.Suitable approximations or equivalents may be provided in the electronbeam to give the desired results. For example,

the electron beam may be composed of short different axial sections, orsections having different electron concentration densities to provide anoverall effect similar to a tapered beam.

The electron beam of this invention need not be tapered as it passesthrough the terminating cavity section of 28. However, the electron beamshould be tapered over all or a substantial number of the tapered cavitysection in tapered section 27. The taper should extend at least overabout three successive tapering cavities and preferably over alltapering cavities. For higher overall efliciency gain and bandwidth itis preferable that the log periodic factor p be substantially similarfor the beam as well as the interaction structure and with the beamsubstantially filling the defined beam channel. However, lesser pfactors may be employed for the beam.

Means to change the cross section or provide taper of an electron beamare well known in the art. These may include magnetic electrostatic orelectromagnetic or other electrical field focusing arrangements whichprovide the proper controlling action on the beam. In one form of thisinvention an electrical focusing solenoid 103 is employed which extendsaxially along the beam path 57. Solenoid 103 includes a tapered section104 lying along the tapered section 27 of the amplifier 10, and thecylindrical section 105 lying along the termination cavity section 28.The number of turns or turn density of the coils of solenoid 103 is alsovaried along the tapered section in conformance with the taper of beam101 to provide a beam taper which is desired. The turn density of thesection 104 increases to a maximum at the cylindrical section 105 andthereafter the beam is cylindrical under the action of a uniformmagnetic field. In utilizing a solenoid coil, the coil itself may betapered or conical to provide a stronger magnetic field progressivelytherealong in correlation with the desired beam taper. For example,either a tapered or cylindrical coil may be employed where the number ofcoil turns or turn density progressively varies by increasing ordecreasing toward one end of the klystron.

Permanent magnet focusing or control is equally applicable to thisinvention and may include one or more magnet assemblies arrayed alongthe axis of the klystron to provide increasing magnetic field strengthtoward one end of the device. A number of electromagnets, permanentmagnets, or electrostatic focusing means or combinations thereof, may beemployed to provide tapering of a beam whose final diameter, or thediameter in the cylindrical section 28 is for example about four timesless than the diameter of the beam entering for example drift tube 40.Periodic focusing devices providing a series of straightlineapproximations of a taper or other intermediate configurations such asscalloping effects may also be employed in this invention.

Applying the log periodic principle to the beam by tapering, togetherwith a tapering beam channel provides the log periodic principle in allsignificant portions of the device which cooperate for power output.This unification indicates a more efficient device and accordinglyincreased bandwidth.

A transmission line 106 or other similar coupling means is employed tocouple power into and out of the klystron amplifier 10. For example, atransmission line is illustrated in FIG. 1 in the form of anelectrically conductive rod 107 which passes through the transversewalls of successive cavities in the klystron amplifier 10. At the inputend 38, device 10 includes a convenient tubular input section 108through which rod 107 passes. Rod 107 is also electrically insulatedfrom tubular portion 108 by means of a ceramic window type seal 109therebetween. At the output section 39 there is also provided a tubularoutput section 108' and ceramic window seal 109'. Rod 107 is alsoconveniently insulated from each of the partition walls through which itpasses so that it is electrically insulated entirely from klystrondevice 10. A number of 7 loop type couplers may also be employed in thisinvention in lieu of the transmission line as described.

Ordinarily in the operation of the device of this invention the electrongun 85 is suitably energized to provide a significantly tapered beam 101passing through successive cavities and interaction gaps for collectionby collector 86. A power signal of given frequency is coupled intodevice 10 through rod 107 at the input or cathode end 38 of device 10.By means of rod 107 the input signal enters the tapered section 27 andselectively energizes a first region of one or more cavities thereinwhose resonant frequencies closely correspond to the frequency of theinput signal. Strong interaction in a klystron manner takes place in theinteraction gaps associated with these cavities and energy is coupled tothe beam. At a further region along the interaction structure one ormore cavities become receptive to beam power and the power from the beamis coupled back to the transmission line as amplified power output. Theterm region is employed to denote a part or section of an axiallyextending interaction structure and constitutes the selected one or moreresonant cavities which are responsive to an input signal.

As a further example, a higher frequency signal progresses down rod 107passing by one or more of the larger cavities which may not be resonantat the frequency of the input signal, until it reaches a portion orregion of device 10 in the tapered section 27 thereof where cavities arenear their resonance at the frequency of the input signal. These lattercavities which have become selectively responsive based on inputfrequency become effective in the known manner and strong interactiontakes place in the affected interaction gaps associated with thesecavities. As the input signal progresses further toward the smaller endof the device into section 28 cavities which are also not resonant, theinteraction diminishes preferably to a negligible level. the amplifiedsignal is then coupled out of device 10 through the rod at the outputend.

The operation of this invention may be alternately described as follows.At a specified frequency one unit of power traveling along asemi-infinite length of the cold structure (or a properly terminatedfinite length) produces a particular pattern of voltage at eachinteraction gap. If the applied frequency is divided by p, thelogarithmic progression, the entire pattern is moved one section to theright or toward the smaller end of the device. Provided that the beamdiameter is scaled by p at each section while the total current andvoltage remain constant, the electron beam behavior scales in the samemanner as the circuit behavior. For a circuit of the type shown in thefigure, interaction between the circuit wave and the beam will takeplace primarily in the portion of the tube where the resonantfrequencies of the cavities are close to the applied frequency. In thisregion the cold circuit is nonpropagating and the signal is coupled fromcavity to cavity by the electron beam in the manner of a klystron. Asthe frequency is increased this active portion moves toward the smallerend of the tube where the beam couples the amplified signal to thecircuit for power output. If the tube is sufficiently long, the inputand output connectors will be located in regions of weak interaction forall frequencies in the desired band. Thus, the end effects are notserious and the gainfrequency response repeats itself each time thefrequency is divided by p. If the diameter of the cylindricalterminating section 28 is sufficiently small electrically at the highestoperating frequency, it is essentially an exact mathematical equivalentfor the conical section it replaces.

It is not necessary in all instances to have the coupling means ortransmission line 106 operatively engage all of the individual cavities.A modification 110 of this invention is illustrated in FIG. 2. In FIG. 2the partial axial section of the interaction structure is a part of thetapered section 27 of FIG. 1. All other remaining parts and structuresare similar to those of FIG. 1. In FIG. 2, the transmission rod 107interconnects or is connected to such cavities as 111, 112, 113 and 114,while cavities 115, 116, 117 and 118 are not connected to thetransmission line. The arrangement is one of having alternate cavitiesconnected to the transmission line. The object of having a number ofuncoupled resonant cavities included in a group of resonant cavitiescoupled to a transmission line is to provide a greater number ofcavities responsive to the frequency of the input signal. The alternateratio may be 1-1, as illustrated, 12, 22 or any other desirable ratiowhich will provide increase in efficiency and gain.

The operation of this device may be best described with reference to amodified W/BL or frequency phase shift characteristic curve asillustrated in FIG. 3. Referring now to FIG. 3 which representsinformation utilized in a successful computer example, the lefthand sideof the diagram shows the phase shift characteristics of a uniform line.As all of the sections have similar shapes, the same diagram applies toany section if the proper frequency scale is used. The righthand portionof the diagram allows the proper frequency scaling for each section tobe determined directly. The nonpropagating region of the diagram occurswhen the cavities are near their resonant frequency. Consider forexample the performance of this device at 2100 megacycles. An input ordrive signal introduced in section 11 travels to section 17 where it isreflected since the structure no longer propagates at this frequency. Inthe vicinity of section 13, Where the circuit impedance is relativelyhigh, the reflected input wave is synchronous with the electron beam,and a strong bunching interaction takes place. The reflected wave issynchronous with the backward wave branch of the W/BL characteristic atpoint A, FIG. 3. From section 18 to section 28 there is no circuitpropagation but as the beam current grows a strong interaction betweenthe beam and the uncoupled cavities takes place. In the operation of thedevice of FIG. 2, because of the log periodic nature of the circuit theresonant frequency of the uncoupled but loaded cavities increases as onemoves toward the output end of the tube. Thus the tuning pattern ofthese uncoupled cavities is similar to that found in conventionalmulticavity klystrons. In section 28 the circuit again propagates in theforward wave mode of the lower branch of the W/BL curve and the bunchedelectron beam delivers power to this output circuit which is formed bythe sections from number 28 to the end of the tube.

A further modification of this invention is illustrated in FIG. 4.Referring now to FIG. 4, there is shown a traveling wave tube 120incorporating the log periodic principle of this invention. As describedfor FIG. 1, an electron gun structure and solenoid 103 provides atapering electron beam passing through a typical helix structure 121 oftraveling wave tube to a collector 86. The helix structure includes thelog periodic principle having turns which decrease in diameter towardone end of the device, and at the same time the turn density or numberof turns per unit length increasing toward the same end of the device.As also described with respect to FIG. 1, the log periodic concept maybe suitably approximated by a number of diminishing straightlinestructures'or other means which affect interaction in the log periodicmanner. Since continuation of the log periodic principle leads to atheoretically infinity tapering helix, the device may be suitablyterminated by a short cylindrical section of helix 122 similar infunction to a cylindrical section 28 of FIG. 1, or a tapered section ofconstant helix. As described for FIG. 1, it is preferred that the remoteor output end 122 of the helix 121 be at about the point where the helixwould ordinarily have provided an apex if imaginary lines be drawn alongthe sides thereof to intersect at a projection point. The terminationstructure in this or preceding embodiments may also include the logperiodic principle.

The overall or general traveling wave tube operation of the device ofFIG. 4 is the same as for other traveling wave tubes. However, the logperiodic principle may be applied to helix, interdigital, as well asother traveling wave tube structures and the beam aifects the operationof the device in a manner similar to the effect as described for theklystron device in FIG. 1. For erample, an input signal of a givenfrequency is introduced in the helix structure and selectively energizesa portion or region thereof responsive to the frequency of the inputsignal. Strong interaction at this region takes place and energy iscoupled to the beam. This energy is coupled out of the beam at a regionof the helix further advanced along the helix at a region Where theamplified signal may again be passed to the helix. The helix interactionstructure is one example of numerous similar and equivalent slow wavestructures known in the art, for example, see US. Pats. 2,843,797 Boydand 2,860,280 McArthur. The helix circuit is included by definition inthose circuits which periodically interact with an electron beam, each iturn of the helix being considered a period.

In the foregoing exemplary applications the electron beam is subject tosome modulation whether velocity, density, or combination thereof. Theinvention is broadly applicable to beam devices where the beam passingthrough a structure provides significant changes in an input signal andpower output may be amplified or provided with desired oscillations. Aswell known in the art, these devices may also act as frequencyconverters, rectifiers, variable conductors, etc.

This invention thus describes the specific combination of a log periodicinteraction structure whether of the coupled cavity resonator type,magnetron or vane type, helix type, or other known circuits, togetherwith a log periodic electron beam passing through the device, where thebeam efiective interaction characteristics vary axially therealong in alog periodic manner. In the operation of such a device the inputfrequency predeterminedly selects its own cavity or cavities or regionof a helix or other interaction structure for interaction. The locationor position of the actual cavity or section of an interaction circuitenergized may change or move along the inter action structure reversiblydependent on input signal frequency. This may be described as a floatingregion along the interaction structure transiently localized by theparticular frequency of the input signal.

The floating region may encompass one or more successive cavities ofFIG. 1, or a portion of the helix of FIG. 4. In a resonant cavity devicea given signal will pro vide effective response of one or more cavitiesfor interaction energy exchange while other adjacent cavities may beonly slightly or negligibly responsive. Where the beam couples power tothe circuit a similar region of cavities are defined. These regions maybe in effect immediately following each other or they may be spacedapart by cavities of negligible or no response. The Peak response of thetwo regions are spaced apart and their axial spacing is fixedly relatedto each other as depending on the frequency of the input signal, andboth float as above defined. Both regions are adjacent in that noeffectively responsive region is apparent therebetween. The operation issimilar for traveling wave structures such as helix structures,interdigital structures, etc. These latter structures may be consideredto be structures periodically acting on or with an electron beam whereeach turn of a helix, or ring of an interdigital structure is defined asa period.

The log periodic circuit may be adapted for forward or backward wavecharacteristics, and for the backward type the structure is in essencereversed, i.e., the input signal is coupled into input 39 and power iscoupled out of output coupling 38. In this embodiment the terminationsection 28 is eliminated. In a reverse structure, where the interactionstructure is smaller at the cathode end and becomes larger toward thecollector end, the log periodic factor p becomes greater than one.

Best results are obtained in this invention when the log factor isapplied to the total interaction structure, not including theterminating section. However, the log factor need not be the same forall applications. For example, in an alternate arrangement of cavitiessuch as illustrated in FIG. 2, alternate cavities may have different logfactors applied. For the invention of FIG. 1 for example different axialsections may have different log factors applied thereto. Incrementaldilferences in the log factor for example between 0.90 and 1.0 aresignificant with respect to operating results. A factor employed in thisinvention has been 0.925 and one preferred range of factors is fromabout 0.90 to about 0.95.

While this invention has been described with reference to particular andexemplary embodiments thereof, it is to be understood that numerouschanges can be made by those skilled in the art without actuallydeparting from the invention as disclosed, and it is intended that theappended claims include all such equivalent variations as come withinthe true spirit and scope of the foregoing disclosure.

What is claimed as new and desired to be secured by Letters Patent ofthe United States is:

1. A log periodic electron beam device comprising in combination (a) anaxially extending log periodic interaction structure,

(b) means to provide electron beam of progressively varying interactioncharacteristics along its length and extending through said interactionstructure,

(c) means to apply a power input signal to said interaction structurefor energization thereof,

(d) termination interaction means to couple power out of saidinteraction structure,

(e) said termination interaction means to couple power out of saidstructure comprising a section of interaction structure not includinglog periodic interaction,

(f) and electron collector means to collect electrons from said beamafter said interaction.

2. The invention as recited in claim 1 wherein said interactionstructure comprises a periodically loaded slow wave R-F transmissioncircuit.

3. The invention as recited in claim 2 wherein said interaction circuitcomprises a traveling wave tube helix structure.

4. The invention as recited in claim 3 wherein said helix tapers from alarger input end to a smaller output end.

5. The invention as recited in claim 4 wherein said helix isfrustoconical.

6. The invention as recited in claim 5 wherein the turn density of saidhelix increases toward said smaller end.

7. The invention as recited in claim 6 wherein a short cylindricalsection of helix of constant turn density terminates said frustoconicalportion at the smaller end thereof.

8. The invention as recited in claim 7 wherein said cylindrical sectionterminates at a point no further than the projected apex of saidfrustrum.

9. The invention as recited in claim 2 wherein said interaction circuitincludes at least in part, a plurality of klystron type cavities.

10. The invention as recited in claim 3 wherein said interaction circuitincludes at least in part, a plurality of klystron type cavities.

11. The invention as recited in claim 9 wherein at least three klystroncavities are employed.

12. A log periodic power amplifier comprising in combination (a) aninteraction structure having a portion thereof for periodicallyinteracting with an electron beam at different successive regions in alog periodic manner,

(b) means to provide a tapering electron beam in said structure forinteraction therewith at said positions, with said beam taper continuingover a substantial number of successive ones of said regions,

(0) means to couple an input signal into said interac- 1 1 tionstructure so that said signal selectively energizes one of saidsuccessive interaction regions based upon the input frequency of saidsignal for amplification of said signal,

(d) means to couple power output from said structure at a differentpower level from an adjacent region of said interaction structureactivated by said one region,

(e) electron collector means to collect electrons from said beam aftersaid interaction, and

(f) said means to couple power output from said structure including atermination interaction section part of said structure which ischaracterized by having interaction regions of substantially similarinteraction characteristics.

13. The invention as recited in claim 12 wherein said interactionstructure is an extended array of coupled cavity resonators.

14. The invention as recited in claim 12 wherein said interactionstructure is terminated by an axially extending cylindrical interactionsection having equal interaction characteristics therealong.

15. The invention as recited in claim 12 wherein said interactionstructure comprises a combination of a traveling wave helix type circuitand a cavity resonator.

16. The invention as recited in claim 12 wherein said regions comprisecoupled cavity resonators each of which have all significant dimensionssmaller than those of a preceding cavity so that said cavity resonatorsvary in a log periodic manner along said areas.

17. A log periodic electron beam device comprising in combination (a)interaction circuit means defining a tapered electron beam paththerethrough,

(b) said circuit having electron beam interaction characteristicstherealong which vary in a log periodic manner,

(c) means to generate and define a tapered electron beam passnig throughsaid defined tapered beam path in said interaction circuit forinteraction therewith, with the taper in said beam extending along thelog periodic variation of said interaction circut in the same nestingdirection,

(d) means to couple a power input signal to said interaction circuit toselectively energize a first region thereof based upon the frequency ofsaid input signal, whereby power is coupled from said tapered beam tosaid circuit at an adjacent region fixedly related to said first regionby said input frequency,

(e) said means to couple power output from said circuit comprising acircuit termination interaction section,

(f) means to couple power output from said interaction circuit,

(g) and electron collector means to collect electrons from said beamafter said interaction.

18. The invention as recited in claim 11 wherein said input and outputmeans are provided by a transmission line.

19. The invention as recited in claim 11 wherein said interactioncircuit includes an axially extending array of reentrant cavityresonators whose interaction effect from interaction gap to succeedinginteraction gaps progressively varies in a log periodic manner.

20. The invention as recited in claim 13 wherein each succeeding cavityresonator is smaller than its preceding cavity resonator in log periodicprogression with successively smaller interaction gaps in logarithmicprogression to provide a tapering interaction circuit.

21. The invention as recited in claim 13 wherein said interactioncircuit and said beam path is frustoconical over a substantial portionof its length.

22. The invention as recited in claim 14 wherein means are provided tocouple power into all said cavity resonators.

23. The invention as recited in claim 14 wherein means are provided tocouple power into only alternate ones of said cavities.

24. The invention as recited in claim 15 wherein a cylindrical klystroncircuit is positioned at the smaller end of said interaction structureto provide similar klystron cavities and interaction gaps.

25. The invention as recited in claim 18 wherein the number of cavitiesin said cylindrical section does not exceed the number of cavities insaid interaction circuit.

26. The invention as recited in claim 19 wherein said cylindricalsection terminates with a klystron cavity at a point no farther than theapex projection of said frustoconical section with centerlines passingthrough said cavities.

References Cited UNITED STATES PATENTS 3,020,439 2/1962 Eighenbaum3l53.5

FOREIGN PATENTS 969,886 3/1950 France. 1,175,462 11/1958 France.

OTHER' REFERENCES Log Periodic Transmission Line Circuit, Part 1: OnePort Circuits by Du Hamel et al., IEE'E Tranactions on Microwave Theoryand Techniques, vol. Mtt-l4, No. 6, June 1966, pp. 264-274 relied upon.

HERMAN K. SAALBACH, Primary Examiner S. CHATMON, JR., Assistant ExaminerUS. "Cl. X.R.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 527.976Dated September 8, 1970 Inventor(s) H- L. 'Ihal, Jr.

It is certified that error appears in the above-identified patent andthat said Letters Patent are hereby corrected as shown below:

3. The invention as recited in claim 2 wherein said interactionstructure comprises a traveling wave tube helix circuit.

sums) m? "FEB-231971 MngOfficar mm E. suauxm, .m.

sinner of Patents FORM PO-1050 (10-69) USCOMM DC 376 p9 U S GOVCINHENTPRINTING OFFICE 1', 0-3."!!!

